Chapter 12. Estimates of Norms of Errors in the Conjugate Gradient Algorithm 200 12.1 Estimates of Norms of Errors in Solving Linear Systems 200 12.2 Formulas for the A-Norm of the Error 202 12.3 Estimates of the A-Norm of the Error 203 12.4 Other Approaches 209 12.5 Formulas for the l2 Norm of the Error 210 12.6 Estimates of the l2 Norm of the Error 211 12.7 Relation to Finite Element Problems 212 12.8 Numerical Experiments 214